You know you are in trouble when your narrative requires you to talk about guns or horses. Because of all subjects, guns and horses are the ones where it is least possible ever to do enough research that an expert specialist will not find some technical error to argue with you over.
One of the best pieces of writing advice I have ever heard was that, if you really want to give a character a gun, whatever it is, describe it as "modified". If it's a "modified" 1911 Colt, you have a getout clause for deciding it takes 72-round magazines if the story wants. I kind of took this aboard when it came to horses as well, which is why in the four stories of mine that have characters being mounted for any length of time, in one of them they ride a form of diatryma (terror bird), in one of them the alien animal that serves as a steed is very much not a horse, in one of them the horses are virtual simulations, and in one of them the only horse to appear on-screen has at least a quarter demonic ancestry. Modified horses ftw.
The great thing about writing far-future space opera is how easy it is to avoid horses. (Also, unless like a number of published writers you have a peculiar hang-up with wanting to recreate Napoleonic battles in space, anything to do with sailing ships, which are a good candidate for a third subject on which it is impossible to do enough research.) And in the central culture of the one I am writing now, they have spent sufficient of their history on spacecraft with hulls that using a fire-arm inside could easily puncture that there is a cultural revulsion at the very thought of projectile weapons as visceral and intense as any culture has ever had for any concept (think of the thing that revolts you most in the world of anything any human being has ever done, and that's how they feel about fire-arms); they use other weapons instead, which I can make up safe, in the knowledge that nobody's going to quibble with me on the precise technical details of antimatter-sparked hand-held fusion reactors based on personal experience.
(There are two incidental cultures that use firearms. They have deep and bitter divisions over terminology, so that what one lot calls a magazine, the other calls a clip, and either side will argue their point endlessly. This stops me actually needing to remember which is which.)
